Hi Piotr, Tudor, On Wed, 27 Jun 2018 15:16:03 +0200 Piotr Bugalski <bugalski.piotr@xxxxxxxxx> wrote: > Hello, > > Atmel SAMA5D2 is equipped with two QSPI interfaces. These interfaces can > work as in SPI-compatible mode or use two / four lines to improve > communication speed. At the moment there is QSPI driver strongly tied to > NOR-flash memory and MTD subsystem. > Intention of this change is to provide new driver which will not be tied > to MTD and allows using QSPI with NAND-flash memory or other peripherals > New spi-mem API provides abstraction layer which can disconnect QSPI > from MTD. This driver doesn't support regular SPI interface, it should > be used with spi-mem interface only. > Unfortunately SAMA5D2 hardware by default supports only NOR-flash > memory. It allows 24- and 32-bit addressing while NAND-flash requires > 16-bit long. To workaround hardware limitation driver is a bit more > complicated. > > Request to spi-mem contains three fiels: opcode (command), address, > dummy bytes. SAMA5D2 QSPI hardware supports opcode, address, dummy and > option byte where address field can only be 24- or 32- bytes long. > Handling 8-bits long addresses is done using option field. For 16-bits > address behaviour depends of number of requested dummy bits. If there > are 8 or more dummy cycles, address is shifted and sent with first dummy > byte. Otherwise opcode is disabled and first byte of address contains > command opcode (works only if opcode and address use the same buswidth). > The limitation is when 16-bit address is used without enough dummy > cycles and opcode is using different buswidth than address. Other modes > are supported with described workaround. > > It looks like hardware has some limitation in performance. The same issue > exists in current QSPI driver (MTD/nor-flash) and soft-pack (bare-metal > library from Atmel). Without using DMA read speed is much worse than > maximum bandwidth (efficiency 30-40%). Any help with performance > improvement is highly welcome, especially for NAND-flash memories which > offers higher capacity than NOR-flash used with previous driver. > > Best Regards, > Piotr > > v2 changes: > - driver is now replacement of existing atmel-quadspi > - code was re-written to follow original code structure > - deinitialization order fixed > - empty atmel_qspi_adjust_op_size function removed > - code formatting fixes > - use spi_device->max_speed_hz to get spi speed > - spi freqency set in spi_controller->setup() hook > - address range checkng for 4-bytes addressing > - use timeout to avoid infinite waiting IIRC, this version was almost ready to be merged except for the missing ->get_name() implementation which should be easy to add. Can one of you post a new version of this patchset? Thanks, Boris
